This NIH-funded study is designed to determine the effects of endurance exercise on muscle protein synthesis in humans; determine whether the effects of endurance training and cardiovascular fitness are modulated by age and to determine the effect of endurance training on the body. Subjects are studied on two occassions with a three-month interval between study dates which involves visits to the GCRC exercise facilities 4-5 times per week and weight monitoring. This study is closed to new participants. Since December 3, 1997, no new participants were enrolled in the study. Six participants have completed the study for a total of 78 completed participants. Ninety-six participants were approved for this study. Analysis of the samples and data is currently underway. GCRC Immunochemical Core Laboratory has completed the analysis. Analysis from the GCRC Mass Spectrometry Lab and Dr. Nair's Lab is in progress.